High precision linear motion component is the motion reference for CNC machine tool, machining center and CMM. It plays a significant role in maintaining the machining accuracy and measuring accuracy of these equipments. There are six motion errors for a linear motion component, which are three linear displacement errors, including position error, horizontal straightness error and vertical straightness error, and three angular displacement, including pitch, yaw and roll. These errors greatly affect the accuracy and quality of these equipments. Therefore, accurate measurement and effective compensation of these errors are the key to the precision manufacture and measurement.
Commonly, the interferometer is employed to measure these errors. However, only one error component can be measured during each adjustment. Furthermore, different attachments and re-adjusting the interferometer are needed in each measuring process. As a result, the measurement efficiency will be reduced, and the measurement accuracy cannot be guaranteed.
U.S. Pat. No. 4,804,270 discloses a five degree of freedom simultaneous measurement system based on the planar diffraction grating. However, the measurement accuracy is comparatively low, and the position error cannot be measured. Moreover, it is not convenient for in-situ measurement due to the cable connection on the moving sensor head.
U.S. Pat. No. 6,049,377 discloses a five-axis/six-axis measurement system. Five or six degree of freedom errors can be measured simultaneously. However, the measurement accuracy of roll is low, and it is not convenient for long distance measurement due to the cable connection on the moving sensor head.
U.S. Pat. No. 5,798,828 discloses a five degree of freedom measurement system using two lasers. However, the system is not suitable for dynamic measurement in high speed machining due to the large volume moving target. In addition, the position error cannot be measured.
Qibo F, Bin Z, Cunxing C, et al. discloses a six degree of freedom simultaneous measurement system. The system is accomplished by combinational method of homodyne interferometer for position error measurement and laser collimation for other five errors measurement. However the measurement accuracy is affected by the beam drift caused by the heat radiation of the laser. (see Development of a simple system for simultaneously measuring 6DOF geometric motion errors of a linear guide[J]. Optics express, 2013, 21(22): 25805-25819).
In general, there are some disadvantages in prior art for six degree of freedom simultaneous measurement as follows: the measurement accuracy is influenced by the heat generated by the laser source which is integrated in the measuring unit; the measurement accuracy of position error, which is measured by homodyne interferometer, is greatly influenced by the measuring environment due to the using of single-frequency laser; it is not convenient for long distance measurement due to the cable connection in moving unit; and the measurement accuracy is influenced by laser beam drift, which is not considered in prior art.